1. Field of the Invention
The present invention relates to a motorcycle mounted with a fuel cell.
In addition, the present invention relates to a stack structure of a fuel cell in which a stacked body of power-generation cells is accommodated in a box-shaped casing, each power-generation cell having an electrolyte-electrode structure and a pair of separators between which the electrolyte-electrode structure is interposed.
Moreover, the present invention relates to a fuel cell having a valve for adjusting a pressure of an exhaust gas generated through a reaction in a fuel cell.
2. Related Art
Most of motorcycles use an internal combustion engine as a driving source. However, from the view point of environmental protection or the like, there have been developed motorcycles which are mounted with fuel cell so as to be driven by the use of electric energy obtained from the fuel cell.
The fuel cell of such a kind of motorcycle includes a fuel cell stack in which a plurality of unit fuel cells is stacked. Power generated from the fuel cell is supplied to an electric motor, thereby driving a wheel of the motorcycle.
The fuel cell generates electric power by a chemical reaction between hydrogen as the fuel gas and oxygen as the reactant gas. Accordingly, a hydrogen supply pipe for supplying hydrogen and an oxygen supply pipe for supplying oxygen are provided in such a kind of motorcycle.
In recent years, a size of the fuel cell has been increased to enhance power generation ability. Thus, the motorcycle requires a considerable space for mounting the large-sized fuel cell.
In a related art of the present invention, as shown in FIG. 22, in such a kind of motorcycle, a head pipe 2a is disposed in a front upper portion of a motorcycle body 1 and a steering axis 3 is rotatably inserted into the head pipe 2a. A handlebar 4 for steering the traveling direction of the motorcycle body is connected to the upper end of the steering axis 3. A front fork 2b is connected to the lower end of the steering axis 3 and a front wheel 5 is axially supported by the lower end portion of the front fork 2b. 
A seat 6 on which a driver sits is fitted to the longitudinal center of the motorcycle body 1 approximately and a fuel cell 7 is mounted to the front lower side of the seat 6. A rear wheel 8 is axially supported in the rear portion of the motorcycle body 1, and the rear wheel 8 is driven by an electric-powered unit 9 disposed in a rear side of the fuel cell 7. Such a related example is disclosed in JP-A-2002-187587.
However, in the motorcycle of JP-A-2002-187587, since the fuel cell 7 is arranged in a front side of the seat 6 on which a driver sits, a lateral side portions of the fuel cell 7 are protruded from a lateral sides of the motorcycle body 1 at driver's foot setting positions, thereby reducing the foot setting space. Accordingly, it is difficult to improve a foot comfort.
Since the increase in size of the fuel cell 7 causes the increase in weight, a center of gravity thereof is moved when the fuel cell is disposed in the front side below the seat 6.
By the way, a polymer electrolyte fuel cell (PEFC) includes a power-generation cell in which an electrolyte membrane—electrode structure (MEA: membrane-electrode assembly) in which an anode and a cathode are disposed on both sides of an electrolyte membrane formed out of a polymer ion exchange film is sandwiched by separators. Generally, a predetermined number (for example, several tens to several hundreds) of power-generation cells are stacked in a stacked body for use so as to obtain desired power from a fuel cell. In the stacked body of the power-generation cells, it is necessary to satisfactorily pressurize and hold the power-generation cells so as to prevent increase in internal resistance of the fuel cell or deterioration in ability of sealing reactant gas. A technology of constructing a fuel cell stack by accommodating a stacked body of power-generation cells in a casing with the power-generation cells compressed in the stack direction is disclosed in JP-A-2005-123114.
FIG. 23 is an assembly diagram illustrating a first structural example of a related fuel cell stack. The fuel cell stack 200 basically includes a power-generation cell stack 201 and a hexahedral box-shaped casing 202 that accommodates the power-generation cell stack 201. The casing 202 is constructed by coupling a first end plate 211 located at one end in a stack direction of the power-generation cell stack 201, a second end plate 212 located at the other end in the stack direction, and first to fourth side panels 213, 214, 215, and 216 disposed on four planes other then the ends in a box shape. Medium supply holes 217 for supplying fuel gas or reactant gas to the power-generation cell stack 201 are formed through the first end plate 211.
Four edges of the first and second end plate 211 and 212 are subjected to an interdigitation machining and only two edges of the first to fourth side panels 213 to 216 connected to the edges of the first and second end plates 211 and 212 are subjected to the interdigitation machining so as to be coupled to the edges of the first and second end plates 211 and 212 in an interdigitating manner. The first and second end plates 211 and 212 and the first to fourth side panels 213 to 216 are connected to each other by coupling the interdigital grooves to each other in the interdigitating manner and inserting shearing pins 218 into them.
FIG. 24 is an assembly diagram illustrating a second structural example of the related fuel cell stack, where like reference numerals denote like elements.
The power-generation cell stack 201 is kept in the compressed state by coupling the first end plate 221 located at one end in the stack direction and the second end plate 222 located at the other end in the stack direction to each other with a plurality of bolts 223.
In the structure employing the shearing pins 218, as illustrated in FIG. 25, since a diameter R2 of pin holes 219 should be greater than a diameter R1 of the shearing pins 218 in consideration of dimension margin at the time of assembling the casing, a gap 220 occurs between the first and second end plates 211 and 212 and the first to fourth side panels 213, 214, 215, and 216. As a result, the pressure between the power-generation cells is not uniform, thereby deteriorating power-generation efficiency.
In the structure employing the connection bolts 223, since spaces for the bolts should be secured on the circumference of the power-generation cell stack 201, the fuel cell stack is increased in size. In this structure, the end plates 221 and 222 are fixed to each other and are also strongly fixed to a vehicle body, and the inside thereof is filled with a metal member (power-generation cells). Accordingly, when a large acceleration acts in the stack direction of the power-generation cell stack 201, gaps are formed between the end plates and the ends of the power-generation cell stack 201. When the gap is formed on the side of the first end plate 221 provided with the medium supply holes 217, the sealing ability between the end plate 221 and the power-generation cell stack 201 may be deteriorated.
Further, in a vehicle such as a motorcycle, a throttle valve is disposed in an air supply passage so as to adjusting an engine output in response to operation of an accelerator and the opening and closing of the throttle valve is performed with the operation of the accelerator.
In recent years, the amount of air supplied to an engine could be more suitably set depending upon traveling conditions of the vehicle by adjusting the opening and closing of the throttle valve by the use of a controller and a motor. In this case, the opening ratio of the throttle valve is detected and fed back by a predetermined sensor and is controlled by the controller to a predetermined target opening ratio.
An example of the throttle valve for performing the opening and closing control thereof by the use of the motor is disclosed, for example, in JP-A-11-343878. The disclosed throttle valve performs the opening and closing control of an air supply pipe by revolving a butterfly valve through a deceleration gear train under control of a predetermined controller. In this case, a potentiometer is provided in a final-stage gear disposed on a rotation axis of the butterfly valve and a feedback control is performed by detecting an amount of rotation of the rotation axis and sending the detected amount of rotation to the controller. The potentiometer includes a brush disposed on a side surface of the rotation axis and a resistor disposed on a substrate opposed to the brush. The amount of rotation is detected by allowing the brush to slide on the resistor.
Further, a gas circulating pump system for a fuel cell is disclosed in JP-A-09-259912. In the system disclosed in the document, hydrogen gas and air are supplied to the fuel cell from a hydrogen gas supply unit and an air supply unit. The hydrogen and the oxygen having passed through the fuel cell flow to the exhaust side through corresponding pressure control valves. The internal pressure of the fuel cell can be controlled by providing such pressure control valves. For example, when the pressures of hydrogen and oxygen supplied to the fuel cell are varied, the power generation of the fuel cell can be kept in a predetermined value. Accordingly, it is considered that the valve system disclosed in JP-A-11-343878 is applied to the pressure control valve of the fuel cell system disclosed in JP-A-09-259912.
However, in the throttle valve disclosed in JP-A-11-343878, since the amount of rotation of the rotation axis is detected by the potentiometer, the detection signal is an analog signal and thus electrical noise can be added thereto. When the feedback control is performed on the basis of the analog signal to which the electrical noise has been added, slight variation may occur in the butterfly valve.
Accordingly, when the valve disclosed in JP-A-11-343878 is adopted for the fuel cell system disclosed in JP-A-09-259912, it is difficult to accurately control the internal pressure of the fuel cell, thereby varying the power generation amount of the fuel cell.